Efficiency Of Solid Oxide Fuel Cell Research Articles

Computational and Experimental Research on the Influence of Supplied Gas Fuel Mixture on High-Temperature Fuel Cell Performance Characteristics

Currently, the process of creating industrial installations is associated with digital technologies and must involve the stage of developing digital models. It is also necessary to combine installations with different properties, functions, and operational principles into a single system. Some tasks require the use of predictive modeling and the creation of “digital twins”. The main processes during the fuel cell modeling involve electrochemical transformations as well as the movement of heat and mass flows, including monitoring and control processes. Numerical methods are utilized in addressing various challenges related to fuel cells, such as electrochemical modeling, collector design, performance evaluation, electrode microstructure impact, thermal stress analysis, and the innovation of structural components and materials. A digital model of the membrane-electrode unit for a solid oxide fuel cell (SOFC) is presented in the article, incorporating factors like fluid dynamics, mass transfer, and electrochemical and thermal effects within the cell structure. The mathematical model encompasses equations for momentum, mass, mode, heat and charge transfer, and electrochemical and reforming reactions. Experimental data validates the model, with a computational mesh of 55 million cells ensuring numerical stability and simulation capability. Detailed insights on chemical flow distribution, temperature, current density, and more are unveiled. Through a numerical model, the influence of various fuel types on SOFC efficiency was explored, highlighting the promising performance of petrochemical production waste as a high-efficiency, low-reagent consumption fuel with a superior fuel utilization factor. The recommended voltage range is 0.6–0.7 V, with operating temperatures of 900–1300 K to reduce temperature stresses on the cell when using synthesis gas from petrochemical waste. The molar ratio of supplied air to fuel is 6.74 when operating on synthesis gas. With these parameters, the utilization rate of methane is 0.36, carbon monoxide CO is 0.4, and hydrogen is 0.43, respectively. The molar ratio of water to synthesis gas is 2.0. These results provide an opportunity to achieve electrical efficiency of the fuel cell of 49.8% and a thermal power of 54.6 W when using synthesis gas as fuel. It was demonstrated that a high-temperature fuel cell can provide consumers with heat and electricity using fuel from waste from petrochemical production.

Facile and Low Temperature Synthesis of Nd1.8Sr0.2NiO4-δ Cathode Nanofibers for Intermediate Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are usually operated at high temperatures (800-1000 °C). As the overall efficiency of SOFC is governed by thermodynamics and kinetics during operation, reducing the operating temperature to 500-650 °C causes significant increase in the electrode polarization losses especially at cathode due to high activation energy towards oxygen reduction reaction (ORR) at cathode, which eventually reduces the overall cell performance. Addressing increased polarization losses at relatively low temperatures (500-650 °C) has been the key issue and a focus of many groups over past couple of decades. Conventional cathode materials lose their ORR activity and so discarded for intermediate temperature (IT)-SOFC application. In this regard, mixed ionic-electronic conductors (MIECs) offer high thermal and chemical stability along with high oxygen diffusion and good electronic conductivity at IT [1,2]. In addition, Ruddlesden-Popper (RP) type MIECs with A2BO4 structure have been demonstrated as promising cathode for IT- SOFCs due to their unique structure, rapid oxygen surface exchange kinetics, and excellent stability in atmosphere. Particularly Nd2NiO4+δ oxides offer an excellent oxygen diffusion coupled with high surface exchange coefficients and comparable thermal expansion coefficients with those of oxygen-ion conductors (YSZ and CGO) [2]. Enhanced electronic conductivity and electrochemical performance have been demonstrated for partial replacement of Nd with Sr in our previous reports [3].Albeit, the intrinsic material properties such as electrochemical catalytic activity and electrical conductivity are of primary importance, an actual electrode performance strongly depends on its microstructure. Therefore, in addition to using high catalytic and conductive materials, achieving an extremely high-power density, thus, requires a finely controlled electrode microstructure, to expand the electrochemically active triple-phase boundary (TPB). Recently, electrospinning has been considered as an efficient, cost effective and promising method for synthesis of ceramic nanofibers. Pertinent literature suggests that SOFC with cathode nanofiber has superior/better performance (nearly doubled power density and significant reduced polarization resistance) compared to powder type electrodes. Selection of suitable cathode materials with modified microstructure (nanofibers) would facilitate more electrochemically active sites for the oxygen reduction at relatively low temperatures <650 °C.In this paper we synthesized Nd1.8Sr0.2NiO4-δ (NSNO) cathode nanofibers using electrospinning technique and compared its electrochemical performance with NSNO nanopowder. Practically, 10 wt.% Polyvinylpyrrolidone (PVP) solution was prepared by dissolving it in ethanol, to which stoichiometric amounts of Nd-nitrate, Sr-nitrate, Ni-nitrate (total weight percentage of metal salts- 3 wt%) were added, together with some deionized water. The mixture was then stirred for 10 h at room temperature on a magnetic stirrer to obtain a homogeneous sol. The sol was loaded into the electrospinning syringe. Distance between the spinneret and the collector was fixed at 25 cm and the high-voltage supply was maintained at 30 kV. The spinning rate was controlled at 5 ml h- 1 by a syringe pump. The obtained nanofibers were dried at 80 °C for 12 h, then sintered at 900 °C for 2 h in air to obtain single-phase NSNO.The obtained nanofibers were characterized using room temperature XRD, XPS, SEM and dc electrical conductivity (400-650 °C). In addition, electrochemical impedance spectroscopy studies on symmetric cells were carried out as a function of temperature (400-650 °C). Improved electrochemical performance is attributed to enhanced electrochemical active sites for ORR due to nanofibers and optimum porosity.

Optimizing fuel transport and distribution in gradient channel anode of solid oxide fuel cell

Precise geometrical adjustment of an anode is crucial for optimizing the performance of solid oxide fuel cell (SOFC). Fuel gas components of SOFC, including H2, CH4, CO, CO2 and H2O, are complex in composition but play a significant role in determining the efficiency of SOFC. This study examines the fuel transport and distribution and the resultant SOFC performance by constructing various gradient channel anode (GCA) structures. The findings show that compared to the traditional un-gradient channel anode (un-GCA) cell, the GCA cell results in more uniform gas distribution and better diffusion of fuel gases, particularly H2, CH4 and H2O. Because of the improved gas diffusion in the anode electrode, the GCA (12 μm) cell exhibits a 2.34 % improvement in power density compared to the un-GCA cell at 800 °C and 0.6 V. Additionally, after increasing the mole fractions of H2 and CH4 in the fuel gas, the power density of the GCA (12 μm) cell is improved by 2.42 % compared with that of the un-GCA cell under the same condition. This study provides clear evidence that incorporating the gradient channel structure in the anode can effectively enhance gas transport, minimize localized gas aggregation and eventually improve the performance of SOFC.

A comprehensive review on durability improvement of solid oxide fuel cells for commercial stationary power generation systems

Solid oxide fuel cells (SOFCs) are recognized as an alternative for power generation applications due to their high efficiency and environment-friendly behaviour. The electronic devices and power age could be revolutionized with the commercialization of such devices. Stationary power generation systems based on SOFCs are a step closer to commercialization due to the latest developments in the technology that promises to overcome the inherent bottleneck of high-temperature fuel cells, i.e., durability. According to the US Department of Energy (DOE), the stationary power generation system should have a lifetime of 40,000 h continuous operation. The efficiency of SOFCs is mainly dependent on their components such as anode, cathode, interconnect, and electrolyte. There are numerous factors affecting the efficiency of SOFCs that include the composition of the fuel, kinetics, and thermodynamics of the cell, and working temperature. In this paper, we have presented a comprehensive review of the recent developments to produce durable SOFCs for commercial stationary power generation systems. The review summarizes several prominent degradation mechanisms involved in the SOFC components and methods to reduce the degradation process. In addition, the methods and techniques adopted for the degradation analysis are fully demonstrated, followed by a detailed durability diagnostic through in-situ and ex-situ durability testing. The review is complemented by a lucid presentation of future research challenges and the knowledge gaps coupled with potential recommendations to fill the gaps. The new engineering designs, the material development and the new knowledge presented in this study could provide useful guidance for the key stakeholders, policymakers and power generation entities to commercially implement the application of durable SOFCs for stationary power generation.

Efficiency estimation of solid oxide fuel cell integrated with iso-octane pretreating system

The effect of iso-octane pretreatment on the efficiency of solid oxide fuel cell (SOFC) is important for selecting suitable pretreating technology. In this work, oxidation index and equivalent fuel utilization for SOFC with pure iso-octane as fuel and pre-treated iso-octane as fuel are designed in a novel way, and then the stable operating condition and efficiency of SOFC integrated with iso-octane pretreating system are investigated based on the fuel composition and anode gas characteristics. At low temperatures, solid carbon and methane are easy to be formed for iso-octane pretreatment, while H2 and CO are easy to be produced at high temperatures from thermodynamics. Steam reforming of 1 mol of iso-octane can produce 17 mol of H2 and 8 mol of CO, and thus steam reforming of iso-octane has little effect on the efficiency of SOFC. When the O/C ratio is 1.5 and the equivalent fuel utilization is 90%, the electrical efficiency of SOFC is 64.6% for steam reforming of iso-octane if the heat is provided by anode off-gas, which is 10.9% higher than that with the fuel from autothermal reforming of iso-octane and 32.6% higher than that with the fuel from catalytic partial oxidation of iso-octane. Through investigating the effect of iso-octane pretreating technology on the oxidation index of anode gas and real fuel utilizations of SOFC at different equivalent fuel utilizations, the accurate effect of iso-octane pretreatment on the efficiency of SOFC can be calculated and analyzed for iso-octane-fuelled SOFC, which can provide good guidance for the experimental process and practical application of iso-octane-fuelled SOFC.

Efficiency Maximization of a Direct Internal Reforming Solid Oxide Fuel Cell in a Two-Layer Self-Optimizing Control Structure.

Control system configuration is essential for the efficiency performance of a solid oxide fuel cell (SOFC). In this paper, we aim to report a novel two-layer self-optimizing control (SOC) system for the efficiency maximization of a direct internal reforming SOFC, where the efficiency index is defined as the profit of generated electricity penalized by carbon (CO2) emission. Based on the lumped-parameter model of the SOFC, comprehensive evaluations are carried out to identify the optimal controlled variables (CVs), the control of which at constant set-points can optimize the efficiency, in spite of operating condition changes. In the lower SOC layer, we configure single variables as the CVs. The results show that the stack temperature is the active constraint which should be controlled to maintain the cell performance. In addition, the outlet hydrogen composition is identified as the optimal CV. This result differs from several previous proposals, such as methane composition. In the presence of operating condition changes, the set-point of hydrogen composition is further automatically adjusted by the upper SOC layer, where a linear combination of the SOFC measurements is configured as the CV, giving negligible efficiency losses. The cascaded two-layer SOC structure is able to maximize the SOFC efficiency and reduce carbon emission without using online optimization techniques; meanwhile, it allows for smooth and safe operations. The validity of the new scheme is verified through both static and dynamic evaluations.

Analysis of solid oxide fuel cell hybrid power system in marine application for CO2 reduction

The usefulness of a solid oxide fuel cell (SOFC) for a large vessel is evaluated by estimating the amount of CO2 emitted by a crude oil tanker. Conventional and two SOFC hybrid power generation systems are proposed and analyzed. The traditional system consists of five generators and a steam boiler, whereas two SOFC hybrid systems are made up of five smaller generators with additional SOFC power and a steam boiler. The performance of the SOFC is calculated through a zero-dimensional model developed, including electrochemical stack model. The CO2 emission of the SOFC hybrid system is estimated depending on the SOFC capacity, 2.5 MW and 5.0 MW. CO2 emissions in the SOFC hybrid system are 5.4% ∼8.8% lower than in the traditional structure for one round trip sail. The reduction of CO2 comes from two factors; the high efficiency of SOFC and the operations of DF generators at a relatively high load rate. The SOFC hybrid system can be an eco-friendly technology to reduce the CO2 emissions of the large ships.

Brazing manufacturing technology of plate-fin heat exchanger for solid oxide fuel cells

The plate-fin heat exchanger (PFHE) is the core equipment used to achieve the high efficiency of solid oxide fuel cell (SOFC), however, the issues of high-performance brazed joints in the manufacturing of the PFHE have been a challenge due to the poor mechanical properties. This study proposes a brazing manufacturing technology of isothermal solidification with the optimized post bonding heat treatment strategy, to synergistically improve the strength-ductility property and homogenize microstructure of brazed joints, aiming at guaranteeing the high energy efficiency of SOFC. The results show that brazing at 1065 °C for 25 min achieves the complete isothermal solidification and an intermetallic-free joint centerline with numerous borides generating in the diffusion-affected zone. Solution treatment then dissolves large quantities of acicular and blocky borides. The uniformity of grain size and kernel average misorientation distribution is also improved due to recrystallization, which becomes more pronounced after solution aging treatment. In addition, solution aging treatment results in an improvement in the ultimate tensile strength of the brazed joint, which is more prominent than that after solution treatment. However, the increase in elongation after solution aging treatment is smaller than after solution treatment, while still much higher than the as-brazed joint due to the dissolution of boride precipitates and growth of twin boundaries. The results demonstrate that the proposed brazing manufacturing technology not only homogenizes microstructure, but also significantly improves strength and ductility, further promoting the long-life operation of SOFC.

Slightly ruthenium doping enables better alloy nanoparticle exsolution of perovskite anode for high-performance direct-ammonia solid oxide fuel cells

• Slightly Ru doping promotes the exsolution of alloy nanoparticles in perovskite anode. • Ru doping greatly reduces the particle size and increase the amount of exsolved alloy nanoparticles. • Ru doped perovskite anode shows superior catalytic activity for NH 3 decomposition and anti-sintering capability. • DA-SOFCs with Ru doped perovskite anode exhibits a superior operational stability to Ru-free counterpart. Fuel flexibility is one of the most distinguished advantages of solid oxide fuel cells (SOFCs) over other low-temperature fuel cells. Furthermore, the combination of ammonia fuel and SOFCs technology should be a promising clean energy system after considering the high energy density, easy transportation/storage, matured synthesis technology and carbon-free nature of NH 3 as well as high efficiency of SOFCs. However, the large-scale applications of direct-ammonia SOFCs (DA-SOFCs) are strongly limited by the inferior anti-sintering capability and catalytic activity for ammonia decomposition reaction of conventional nickel-based cermet anode. Herein, a slightly ruthenium (Ru) doping in perovskite oxides is proposed to promote the alloy nanoparticle exsolution, enabling better DA-SOFCs with enhanced power outputs and operational stability. After treating Ru-doped Pr 0.6 Sr 0.4 Co 0.2 Fe 0.75 Ru 0.05 O 3-δ single-phase perovskite in a reducing atmosphere, in addition to the formation of two layered Ruddlesden-Popper perovskites and Pr 2 O 3 nanoparticles (the same as the Ru-free counterpart, Pr 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ ), the exsolution of CoFeRu-based alloy nanoparticles is remarkably promoted. Such reduced Pr 0.6 Sr 0.4 Co 0.2 Fe 0.75 Ru 0.05 O 3-δ composite anode shows superior catalytic activity and stability for NH 3 decomposition reaction as well as anti-sintering capability in DA-SOFCs to those of reduced Pr 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ due to the facilitated nanoparticle exsolution and stronger nanoparticle/substrate interaction. This work provides a facile and effective strategy to design highly active and durable anodes for DA-SOFCs, promoting large-scale applications of this technology.

(Digital Presentation) La0.8Sr0.2MnO3-Δ-Based Nanocomposite Functional Layers for Improved Cathode Efficiency in SOFCs

The ongoing energy transition towards the substitution of fossil fuels for renewable and environmentally friendly energy sources, leads to the search for alternative energy conversion systems. In this context, Solid Oxide Fuel Cells (SOFC) are efficient electrochemical devices that are able to convert chemical energy in the form of fuels into electricity [1]. The efficiency of SOFCs at low operating temperatures is mainly limited by the high polarization resistance of the cathode [2], reason why several strategies are being proposed to enhance the electrochemical activity of such electrodes. Among them, optimizing the electrode microstructure by different preparation methods, such as infiltration and spray-pyrolysis deposition, have rendered excellent and durable electrochemical performance [3]. In addition, the tailoring of the electrode/electrolyte interface by incorporating functional layers have proven to be particularly useful to improve electrode properties [4].The present work proposes an alternative approach by the incorporation of several nanocomposite functional layers at the interface between the traditional La0.8Sr0.2MnO3- d (LSM) cathode and the Zr0.84Y0.16O2- d (YSZ) electrolyte. Different compositions that combined LSM with different ionic conductors, i.e. LSM-Ce0.9Gd0.1O1.95 (CGO) and LSM-Bi1.5Y0.5O3 (BYO), were directly deposited by spray-pyrolysis on the YSZ electrolyte in a single step by a co-synthesis method. The nanocomposite functional layers were studied by different structural and microstructural techniques, such as XRD and SEM-EDX. They exhibited lower grain size compared to that of the homologous single phase; specially the LSM-CGO nanocomposite showed improved adherence to the electrolyte without the presence of any crack or delamination, with the lowest grain sizes of 12.54 and 8.56 nm for LSM and CGO, respectively, after annealing at 1000 ºC. SEM images revealed a dense functional layer with a thickness of about 750 nm (Fig 1A). Overall, all functional layers showed a dense structure with excellent adherence to the electrolyte and no chemical reaction could be detected between the cell components.The electrochemical properties of functional layers were also investigated by impedance spectroscopy, distribution of relaxation time, dc-bias and I-V curves. The incorporation of any functional layer reduced the Area Specific Resistance (ASR) values of the cathode, which was associated with a reduced charge transfer resistance and a fast oxide ion transport at the electrode/electrolyte interface as consequence of the good ionic/electronic conductivity of the functional layer. The polarization resistance at 700 ºC was of 1.71 and 0.46 Ω cm2 for the LSM cathode without and with LSM-CGO active layer, respectively (Fig. 1B). The performance of the single cell with LSM-CGO as functional layer, Ni-YSZ|YSZ|LSM-CGO/LSM, revealed maximum power densities of 1.20 and 0.85 W cm-2 at 800 and 700 ºC, respectively, values that were considerably higher than those obtained for the cell without any functional layer, i.e. 0.79 and 0.46 W cm-2.The obtained results confirm the improved performance of SOFCs when tailoring the cathode/electrolyte interface by incorporating a functional layer with nanostructured features and mixed ionic-electronic conducting properties. With that in mind, this research may serve to improve the electrochemical performance of solid oxide cells at intermediate/low operating temperatures without compromising the cell’s integrity.[1] A.B. Stambouli, E. Traversa, A. Stambouli, Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy, Renew. Sustain. Energy Rev. 6 (2002) 433–455.[2] S.B. Adler, Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes, (2004).[3] L. dos Santos-Gómez, E.R. Losilla, F. Martín, J.R. Ramos-Barrado, D. Marrero-López, Novel Microstructural Strategies To Enhance the Electrochemical Performance of La0.8Sr0.2MnO3−δ Cathodes, ACS Appl. Mater. Interfaces. 7 (2015) 7197–7205.[4] V. Zapata-Ramírez, L. dos Santos-Gómez, G.C. Mather, D. Marrero-López, D. Pérez-Coll, Enhanced Intermediate-Temperature Electrochemical Performance of Air Electrodes for Solid Oxide Cells with Spray-Pyrolyzed Active Layers, ACS Appl. Mater. Interfaces. 12 (2020) 10571–10578. Figure 1 . A) Scanning electron microscopy (SEM) image of the LSM cathode deposited onto YSZ with a LSM-CGO nanocomposite functional layer in the electrode/electrolyte interface. B) Impedance Spectroscopy (EIS) test at 700 ºC of the LSM cathode with no functional layer (black), with single-phase LSM as functional layer (red), and LSM-CGO nanocomposite as functional layer (blue). Figure 1

Reduction of operation temperature in SOFCs utilizing perovskites: Review

Fuel cells are electrochemical devices utilized for converting chemical energy to electrical energy. Solid Oxide Fuel Cells (SOFCs) have several advantages over other kinds. For instance, high energy efficiency expanded fuel flexibility, low environmental pollutant emission are the properties of SOFCs that make them superior to other fuel cell types. Due to these special characteristics, SOFCs are gained a great deal of attraction. These fuel cells consist of different main operating parts, a cathode, an anode, and electrolyte which each of them demands special materials to operate with the most efficiency. SOFCs mostly operate in high temperatures (800-1000 ᵒC). Reducing the operating temperature to lower than 600 ᵒC or intermediate temperatures 600-800 ᵒC is one of the methods that can make them more practical devices. Perovskite oxides can be used effectively as all main parts of SOFCs because of their excellent properties like electrical and ionic conductivities, oxygen ion vacancies, great catalytic properties, thermal durability, and chemical stability to decrease the operating temperature. In this review, numerous perovskite-based materials utilized in the anode and the cathode electrodes of SOFCs are investigated in the most recent, advanced, and novel works. The perovskite materials, their properties, and their influence on the fuel cell’s performance, and in some cases the sulfur tolerance of the materials when H2S co-exists in the fuel of the fuel cell are reviewed in this paper Adding different dopants in A-site and B-site of the perovskite oxides is the most effective way to modify the characteristics of the materials. This review can provide great data on the possible perovskite oxides with the capability of enhancing the efficiency of SOFCs by reducing the operating temperature, and their most decisive and significant characteristics, like composition, structure, electrical conductivity, electrochemical and mechanical properties for research groups working on solid oxide fuel cells.

Thermodynamic modeling and exergy investigation of a hydrogen-based integrated system consisting of SOFC and CO2 capture option

The current study deals with the thermodynamic modeling of an innovative integrated plant based on solid oxide fuel cell (SOFC) with liquefied natural gas (LNG) cold energy supply. For the suggested innovative plant the energy, and exergy simulations are fully extended and the plant comprehensively analyzed. According to mathematical simulations of the proposed plant, a MATLAB code has been extended. The results indicate that under considered initial conditions, the efficiencies of SOFC and net power generation calculated 58% and 78%, respectively and the CO2-capture rate is obtained 79 kg/h. This study clearly shows that the integrated system reached high efficiency while having zero emissions. In addition, the efficiencies and net amount of power generation, cooling or heating output and SOFC power generation are discussed in detail as a function of different variables such utilization factor, air/fuel ratio, or SOFC inlet temperature. For enhancing the power production efficiency of SOFC, the net electricity, and CCHP exergy efficiency the plant should run in higher utilization factor and lower air/fuel ration also it's important to approximately set SOFC temperature to its ideal temperature.

Thermodynamic analysis of 100% system fuel utilization solid oxide fuel cell (SOFC) system fueled with ammonia

The system efficiency of solid oxide fuel cells (SOFCs) fueled with ammonia or pure hydrogen always underperforms compared to the SOFCs fueled with carbon-based fuels. Hence, improving the efficiency of SOFCs fueled with pure hydrogen or hydrogen carriers such as ammonia is required to promote hydrogen economy. This study deals with the thermodynamic analyses of SOFC with 100% system fuel utilization configuration achieved by a dead-end anode (DEA) loop. The results are compared with the conventional SOFC configuration with the afterburner setup. It is shown that the energy efficiency and exergy efficiency of ammonia-fueled recirculation system are 12.17% points and 11.39% points higher than the conventional system. Energy balance comparison shows that the reduction in heat loss through exhaust gas is one of the significant factors for improving the system efficiency. The improvement in the exergy efficiency of the recirculation system is attributed to the reduction in exergy destructions in air preheaters and the elimination of exergy destruction at the afterburner. In addition, a parametric analysis and artificial neural network– genetic algorithm (ANN-GA) based optimization are performed to understand the effects of stack fuel utilization, current density, stack operating temperature, radiation loss, the pressure ratio across the membrane, and species removal rate in anode off-gas on system efficiency. The system efficiency as high as 75% lower heating value (LHV) can be achieved by the DEA loop configuration with operating the system at lower stack fuel utilizations.

Thermodynamic modeling of sulfuric acid decomposer integrated with 1 MW tubular SOFC stack for sulfur-based thermochemical hydrogen production

This study developed a thermodynamic model of a set of sulfuric acid decomposers for thermochemical hydrogen production. It was integrated with a 1 MW tubular-type solid oxide fuel cell (SOFC) stack. With the model, we evaluated the feasibility of the combined production of electric power, heat, and sulfur dioxide for thermochemical H2 production. The integrated reactor model consists of three parts: i) SOFC submodel, ii) sulfuric acid decomposition (SAD) submodel, and iii) sulfur trioxide decomposition (STD) submodel with the catalysts Pt/γAl2O3 and WX-1. The efficiency of the integrated system was evaluated at a low-pressure range by polarization and efficiency curves for the SOFC, as well as pinch analysis for the SAD. The highest SOFC efficiency and SO2 production were achieved at 1.25 bar, whereas the lowest fuel consumption and heat demand for SO2 production were achieved at 3.0 bar. Furthermore, WX-1 performed better in the high-temperature range, whereas Pt/γAl2O3 performed better than WX-1 under low-temperature conditions. The Pt-supported catalyst could achieve SO3 conversion of 66% and SO2 yield of 57% at a gas temperature of 1025 K using the proposed integrated reactor design.

Multi-objective optimization of biogas systems producing hydrogen and electricity with solid oxide fuel cells

The design of solid oxide fuel cells (SOFC) using biogas for distributed power generation is a promising alternative to reduce greenhouse gas emissions in the energy and waste management sectors. Furthermore, the high efficiency of SOFCs in conjunction with the possibility to produce hydrogen may be a financially attractive option for biogas plants. However, the influence of design variables in the optimization of revenues and efficiency has seldom been studied for these novel cogeneration systems. Thus, in order to fulfill this knowledge gap, a multi-objective optimization problem using the NSGA-II algorithm is proposed to evaluate optimal solutions for systems producing hydrogen and electricity from biogas. Moreover, a mixed-integer linear optimization routine is used to ensure an efficient heat recovery system with minimal number of heat exchanger units. The results indicate that hydrogen production with a fuel cell downstream is able to achieve high exergy efficiencies (65–66%) and a drastic improvement in net present value (1346%) compared with sole power generation. Despite the additional equipment, the investment costs are estimated to be quite similar (12% increase) to conventional steam reforming systems and the levelized cost of hydrogen is very competitive (2.27 USD/kgH2).

Thermodynamic and exergy evaluation of a novel integrated hydrogen liquefaction structure using liquid air cold energy recovery, solid oxide fuel cell and photovoltaic panels

High specific energy consumption (SEC) and its high cost of manufacturing are among the main problems in the hydrogen liquefaction industry. In this paper, an integrated structure for liquid hydrogen production using liquid air energy recycling, fuel cells, carbon dioxide power generation cycle, and photovoltaic (PV) panels is developed and exergetically assessed. To liquefy the hydrogen gas are utilized six compression refrigeration cycles with hydrogen and helium refrigerants. The compressed liquid air is used for the precooling of the hydrogen liquefaction process. After the cold energy recovery from liquid air, it is heated by the waste heat load of the refrigeration cycle and solid oxide fuel cell (SOFC) and then enters the gas turbine and fuel cell, respectively. The fuel cell output hot stream is used to supply heat to the power generation cycle and preheat the fuel cell inlet stream. This integrated structure generates 1,028 kg/h liquid hydrogen by receiving 60.79 kg/h natural gas and 5.559 MW power from solar panels under the climatic conditions of Yazd, Iran. The specific energy consumption of the hydrogen liquefaction process, SOFC efficiency, and carbon dioxide power generation cycle efficiency are obtained as 5.955 kWh/kgLH2, 62.96%, and 44.06%, respectively. Integrating the refrigeration structure with the process core is performed in the form of hot and cold composite diagrams. The exergy assessment indicates that the highest exergy destruction occurs in solar panels (81.37%), heat exchangers (7.60%), and turbines (4.73%), respectively. The sensitivity analysis demonstrates that the integrated structure exergy and SOFC efficiencies decrease to 52.9% and 62.3%, respectively when the inlet liquid air mass flow rate increases from 7,400 kg/h to 10,200 kg/h. The power supplied by solar panels and SEC of hydrogen liquefaction process increase up to 5,599 kW and 6.1 kWh/kg LH2, respectively with a decrease of pumped liquid air pressure from 80 bar to 40 bar.

Optimization of Methane Reforming for High Efficiency and Stable Operation of SOFC Stacks

: Solid Oxide Fuel Cells (SOFCs) is an efficient and clean pathway to generate electricity. In addition to hydrogen, SOFCs also provide the possibility for the utilization of a variety of carbon containing fuels. However, the application of carbon-based fuels in SOFC remains to be further studied. In this study, an external reformer was used to create appropriate reforming syngas from methanol and avoid carbon deposition. The performance and the efficiency of SOFC were researched with methanol-reformed syngas as fuel. The thermodynamic calculation and experimental work of water vapor reforming reaction of methanol fuel were carried out to study the composition of reforming gas under different temperature and steam-carbon ratio conditions, where the experimental results and the computational results matched well. The mole fraction of hydrogen in reformed syngas was about 55% within the temperature of 700~800 ℃, nevertheless, this value reached 70% if the moisture was removed. Therefore, the reformed syngas should be applied to SOFCs before being condensed and dried. Based on the comparison between the experimental results and the calculated ones, the appropriate components were selected to prepare the reforming syngas, feeding into the anode of SOFC to test the performance and the efficiency. Optimal temperature and steam-carbon ratio conditions for methanol vapor reforming were obtained. Under these conditions, the power density of SOFC exceeded 0.4 W/cm2 and the efficiency reached 50% (LHV). The main conclusions confirmed the high efficiency and feasibility of the methanol-fueled SOFC power generation system.

Anode‐supported solid oxide fuel cells with multilayer LSC/CGO/LSC cathode

AbstractThe multilayer La0.6Sr0.4CoO3/Ce0.9Gd0.1O2/La0.6Sr0.4CoO3 (LSC/CGO/LSC) thin film cathode of the solid oxide fuel cell (SOFC) with the different thickness of the LSC and CGO layers are obtained by magnetron sputtering. Cathodes are deposited onto the NiO/8YSZ anode‐supported 8YSZ/CGO bilayer electrolyte. The influence of the deposited multilayer cathode on the SOFC performance is investigated in the temperature range between 800 and 600°C. It is shown that the thin‐film multilayer cathode allows increasing the SOFC efficiency, and the obtained optimum thickness of the LSC and CGO layers provides the maximum power density for SOFCs. The maximum power density of 2430, 1170, and 290 mW cm–2 is obtained respectively at 800, 700, and 600°C for the SOFCs with the LSC/CGO/LSC layer 50/50/50 nm thick. The polarization resistance measured at 800 and 750°C on the symmetric SOFC with the CGO electrolyte and LSC/CGO/LSC cathode is 0.17 and 0.3 Ω cm2, respectively.

Clean and stable conversion of oxygen-bearing low-concentration coal mine gas by solid oxide fuel cells with an additional reforming layer

Direct power generation using low-concentration coal mine gas (LC-CMG, < 30% CH4) by solid oxide fuel cells (SOFCs) is an attractive approach for the clean and efficient utilization of abundant LC-CMG resources. In this study, Ni–Fe alloy catalyst from in situ decomposition of NiFe2O4 oxide is used to promote the electrochemical performance, efficiency and robustness of SOFCs using simulated LC-CMG as fuel. The modified SOFC is fed with humidified H2 and CH4–N2 in sequence and exhibits high electrochemical performance. There is only a slight performance drop from 783 to 660 mW cm−2 when adding O2 in humidified CH4–N2 fuel. The operation of all cells with different concentrations of LC-CMG is quite stable during over 100-h tests and no coking is found on the entire anode and Ni–Fe alloy catalyst, suggesting the cell with superior resistance to coking. Besides, a heterogeneous reaction model is established to reveal the anti-carbon effect of the Ni–Fe catalyst. Our findings indicate the great application potential of direct power generation from LC-CMG by SOFCs with an additional reforming layer.

Effects of methane processing strategy on fuel composition, electrical and thermal efficiency of solid oxide fuel cell

Natural gas is a cheap and abundant fuel for solid oxide fuel cell (SOFC), generally integrating the SOFC system with methane pre-treating system for improving the stability of SOFC. In this paper, the accurate effects of methane processing strategy on fuel composition, electrical efficiency and thermal efficiency of SOFC are investigated based on the thermodynamic equilibrium. Steam reforming of methane is an endothermic process and can produce 3 mol of H2 and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is high at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is low. On the contrary, partial oxidation of methane is an exothermal process and only produces 2 mol of H2 and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is low at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is high. When the O/C ratio is 1.5, the electrical efficiency of SOFC is 55.3% for steam reforming of methane, while 32.7% for partial oxidation of methane. High electrical efficiency of SOFC can be achieved and carbon deposition can be depressed by selecting suitable O/C ratio from methane pretreatment according to the accurate calculation and analysis of effects of different methane processing strategies on the electrical efficiency and thermal efficiency of SOFC.